A digital broadcast receiving terminal uses a Code Division Multiplexing (CDM) channel to demodulate a received signal. The CDM channel includes three system information channels and two media channels. The system information channels are control channels rather than broadcast data channels. The media channels are channels that carry broadcast service content.
The system information channel includes a pilot channel, a Conditional Access System (CAS) channel, and an Electronic Program Guide (EPG) channel. The receiving terminal (“terminal” or “receiver”) must continuously receive the system information channels, no matter what channel the user views. The receiver must continuously monitor the system information to determine whether or not it has been updated. When the user attempts to receive a digital broadcast, the receiver must first obtain system information in order to allow the user to view a desired channel broadcast.
Using pilot channel configuration information, the receiver can determine which CDM channel contains Program Specific Information (PSI)/Service Information (SI). Such system information items have different transmission periods (or intervals) according to their importance. In order to quickly enter its initial receiving operation, the receiver must quickly obtain information items having a short transmission period.
When a conventional satellite digital multimedia broadcast (DMB) receiver enters an initial receiving operation, the receiver sequentially obtains the pilot channel configuration information, obtains the PSI, a decodes an A/V channel, and the like as illustrated in a flow chart of FIG. 1.
When a user attempts to view or listen to a broadcast (S101), the receiver allows the user to select a channel using a Service Description Table (SDT) that has been stored in order to provide at least channel information such as a channel list and a channel name to the user (S102).
The receiver then achieves pilot channel synchronization (S103). Only after the pilot channel synchronization is achieved, the receiver can properly demodulate the CDM channel.
After achieving the pilot channel synchronization, the receiver first obtains CDM channel configuration information received in a pilot channel and transfers it to a controller (specifically, a Main Processing Unit (MPU)) (S104).
The controller determines a CDM channel which must be demodulated in order to obtain PSI/SI, and starts obtaining PSI/SI (S105).
The receiver obtains the PSI required to demodulate a broadcast channel (specifically, a PAT*, a PMT*, and a CAT* corresponding to a channel actually selected by the user) to extract audio/video and CAS-related PIDS* of the channel actually selected by the user. Applying bit de-interleaving to the satellite DMB causes a time delay of about 3.5 seconds or more after the receiver starts extracting PSI. Using the CDM channel configuration information and PSI, it is possible to determine CDM channels which must be demodulated in order to decode an audio/visual channel corresponding to the channel actually selected by the user (S106).
The receiver starts demodulating the determined CDM channels to provide audio/video to the user (S107). As described above, applying bit de-interleaving to the satellite DMB causes a time delay of about 3.5 seconds or more after the receiver starts extracting PSI. While receiving the broadcast, the receiver continuously monitors CDM channel configuration information and PSI/SI to determine whether or not it has been updated. If the CDM channel configuration information or PSI/SI has been updated, the receiver replaces the previous information with the updated information (S108).
The PSI among the system information (PSI/SI) has a short transmission period since the PSI directly relates to the receiver's operation. The receiver can operate properly only after obtaining the PSI. Service information, which is provided for system operation and user convenience, has a long transmission period.
The pilot channel is used not only to achieve received signal synchronization but also to carry CDM channel configuration information. The CDM channel configuration information is used to indicate configuration information which other channels contain. Specifically, the CDM channel configuration information indicates the CDM channels that carry other PSI/SI and A/V data items. In combination with the PSI/SI, the CDM channel configuration information may be used as a basis for determining which CDM channel must be demodulated to view a given channel number. Accordingly, the receiver operates in the following order. First, the receiver achieves synchronization through a pilot channel. Next, the receiver obtains CDM channel configuration information of the pilot channel and then obtains PSI/SI based on the obtained CDM channel configuration information. The receiver then starts demodulating a CDM channel corresponding to the channel selected by the user.
The conventional digital broadcast receiver usually achieves synchronization through a pilot channel. Thereafter, when the receiver is stabilized, it obtains CDM channel configuration information. The CDM channel configuration information is transferred to the MPU. The MPU analyzes the CDM channel configuration information to obtain PSI/SI. The receiver obtains the PSI after obtaining the CDM channel configuration information. Thus, even in a good wireless environment, a longer time is required to initially receive a digital broadcast than to change channels. Thus the initialization process requires additional time to obtain the CDM channel configuration information and to perform the PSI/SI CDM bit de-interleaving.
In order to quickly achieve synchronization, bit interleaving is not applied to a pilot signal that carries CDM channel configuration information and a digital broadcast synchronization signal. Instead, the pilot channel typically uses transmission power that is about 3 dB (or twice) higher than other channels. However, the pilot channel is vulnerable to burst errors because it uses no bit interleaving. Almost no packet error or bit error occurs in other CDM channels after Viterbi demodulation due to the characteristics of wireless environments. However, many errors occur in the pilot channel since the pilot channel does not use bit interleaving. Thus, in a weak electric field, it is difficult or takes a long time to obtain CDM channel configuration information carried in the pilot channel. For example, when a receiver attempts to receive a digital broadcast in a weak electric field, it may take a long time (or may not be possible) for the receiver to receive the broadcast although a nearby user is able to view a digital broadcast.